Safety pressure relief device



R S. COFFMAN SAFETY PRESSURE RELIEF DEVICE Sept. 2o, 1960 2 Shee'ts-Shee1 Filed Sept. 10 1954 INVENTOR. Roba/* 5. Coffman.A

v BY 5% l ATTORNEY Sept. 20, 1960 Filed sept. 1o, 1954 R. S. COFFMANSAFETY PRESSURE RELIEF DEVICE ATTORNEY 2,953,279 SAFETY PRESSURE RELIEFDEVICE Robert S. Coffman, Kansas City, Mo., assigner to Black,

Sivalls & Bryson, Inc., Kansas City, Mo., a corporation of DelawareFiled Sept. 10, 1954, Ser. No. '455,333

9 Claims. (Cl. Z2089) This invention relates to safety pressure reliefdevices -used to p-rotect pressure vessels. More particularly, thepresent invention relates to safety pressure devices of the rupturable.ldisc type suited to elevated temperatures, fluctuating pressures andcorrosive conditions.

Previous safety pressure devices of the rupturable disc Ytype have notoperated entirely satisfactorily under the .aforementioned extremeconditions. Their operating life -under vthese conditions has beenlimited', particularly where there is a combination of two `or all ofthe condiztions. The limited life of this type of unit under elevatedtemperatures is believed to be 'due to creep failure. The term elevatedtemperatures for the purposes of this description means temperatures atwhich the metal of the disc under the predetermined stress would creepappre- -ciably and ultimately fail within a period of time ofone :monthor less. The limited life ofvthis type of unit under fluctuatingpressures is believed to be due to notch failure. Generally, this type ffailure occurs in rupture discs when they are exposed -to alternatinginternal and Vexternal pressure dierentials. What actually happens tothe disc is that an internal excess pressure differential tends toincrease the crown heightand move the central .portion of the disc awayfrom the vacuum support which vis often supplied to prevent distortionof the disc when pressure within the vessel falls below that on theoutside. With this central portion of the disc moved out of contact withthe vacuum support the disc will be forced back onto the support when anexternal excess pressure differential is imposed on the unit. Thisreversing of the disc will cause wrinkles to be formed which willdevelop into notch failure. Thus within a relatively short period ofytime (for example one month or less) suflicient uctuations may beimposed on .the disc to cause notch or kinking failure. Obviously, thepresence of corrosive conditions either in combination with one or bothof the above mentioned conditions or by itself will tend to decrease theoperating life of the unit appreciably.

Another disadvantage to previous rupturable disc safety y pressurerelief devices is that they inherently have a time "lag between the timewhen bursting pressure is reached and the time when the disc ruptures.The reason for this time lag is that to rupture the disc hask to bestressed beyond the yield point. Thus, even though .the ultimate`strength of the 'disc has been reached, the disc will yield 'beforerupture, causing a lapse of time which may allow additional pressureincreases.

The primary object of this invention is to provide a ysafety pressurerelief device which will give increased operating life under conditionsof elevated temperatures as previously described, fluctuating pressuredifferentials Vand corrosion. Another important object of this inventionis to provide a safety pressure relief device which will withstandseparately, or any combinations of, elevated temperatures, fluctuatingpressures and corrosion, without appreciably affecting the burstingpressure of thel device.

Another object of fthe present invention is 'to provide a dome-shapedsafety pressure relief device having slots States Patent f"ice radiatingfrom a solid central portion for which the rupture pressure may bepredetermined. A still further object of the present invention is toprovide a safety pressure relief device structure composed of twomembers, one determining the rupture pressure and the other sealing thestructure when installed in a relief area of a pressure vessel. Afurther object of the present invention is to provide a safety pressurerelief device composed of two members, one determining the rupturepressure and the other protecting the first member from corrosiveconditions and sealing the structure when installed in a relief area ofa pressure vessel.

Another object of the present invention is to provide a safety pressurerelief device which will not appreciably increase in crown height underconditions of elevated temperature, fluctuating pressure and corrosion,but will remain in position on its vacuum support at all times until therupture pressure of the device is exceeded.

Another object of the present invention is to provide a safety pressurerelief device which will rupture, giving pressure relief immediately,when the predetermined bursting pressure in the vessel or system isreached. A -still further object of the present invention is to providea safety pressure relief device which will rupture at its original crownheight when the predetermined bursting pressure is reached.

In accomplishing these and other objects of the invention, I haveprovided improved details of structure, 'the preferred form of which isillustrated in the accompanying drawing wherein:

Fig. l is a partially sectioned perspective view of a device embodyingthe principles of the present invention.

Fig. 2 is a view illustrating the assembly of the protection elements onthe concave side of the dome-shaped rupture disc.

Fig. 3 is a sectional view of a device embodying the principles of thepresent invention and illustrating itin its ruptured condition.

Fig. 4 is a view illustrating thek components of `the present inventionin'spaced relationship.

The device as shown in Fig. l embodies a preferred Nform of the presentinvention. A base flange Y1 is threaded or otherwise suitably connectedto a pipe or tubularmem- .ber 2 which serves as the relieving outlet forthe Ypressure vessel to be protected. The safety pressure relief device3 and thevacuum support 4 are installed .between the base flange 1 and aholddown flange 5. The holddown flange 5 is generally provided withthreads as shown at 6 or other suitable means of connecting piping (notshown) to Vent the volume of gases away from the vessel area whenrequired. The two flanges 1 and 5 are bolted together by bolts 7, nuts 8and washers 9. The Vsafety pressure relief 4device 3 serves as a gasketbetween the flanges 1 and 5 to provide a ysealed connection for thepressure vessel.

The safety presure relief device 3 is composed of a slotted dome-shapedrupture disc 1l), a sealing member 11 and aplurality of protectionelements 12.. Theelements 12 |are best shown in Fig. 2. They are madefrom relatively thin material and are positioned between the slotteddisc 10 and the sealing member 11 to protectthe sealing member 11 fromcutting itself on the sharp kedges of the slots 13 in the disc 10. Theelements 12 are spot Welded as shown at 14 on otherwise suitably secured,to the disc 10 in covering relationship to the slots 13 in ,the disc10. Care must be taken to prevent securing any .of the elements 12 tobot-h sides of one of the slots 13. These protection elements 12 havebeen yfound helpful Y'in the protection of the sealing member 11butlar-,enotalways necessary. Also another kpossible conliguration ofrla protection member would `be 'to have 'it Yin Vthe shape ship to theslots 13 in the disc 10 with only one petal secured to the member 10.These protection members may be of any desired shape or configuration aslong as they protect the sealing member 11 from the sharp edges ,of theslots 13 in the disc 10 and do not present sharp edges themselvescausing a possible abrading of the seal- .ing member 11. Also, careshould be taken in the design of these protection members so that theydo not alect the bursting pressure nor restrict the relief opening whenoutwardly tapered anchoring ange 17. The at, integral `annularperipheral flange 18 shown in Fig. 4 has no other function than to makethe disc 16 a little easier to handle `and also to provide a surface forthe stamping of the pressure rating of the unit.

'Ihe slots 13 in the disc 1i) extend radially outward from the solidcentral portion 19. At each end of the slots 13 holes 20 and 21 aredrilled or punched to prevent any stress `concentrations at the ends ofthe slots. The holes 21 at the outer end of the slots 13 are positionedin the dome-shaped portion just short of the reversed curve 16.

The device may be constructed to disrupt at a predetermined pressure forany diameter of dome by providing metal of proper thickness, the tensilestrength of the metal being considered and providing the dome with slotsof proper length. The length of the slots 13 and their proximity at the`central portion of the dome will determine the bursting pressure of theunit. For example, the longer the slots, the closer their proximity atthe central portion of the dome, the smaller the area will be betweenthe slots to resist the internal pressure of the vessel.

The sealing member 11 is made to conform with the shape of thedome-shaped slotted disc 10 or must be of suflicient flexibility toassume such shape when assembled as a part of this unit. Since thefunction of the sealing member 11 is simply to prevent leakage throughthe unit 3 and to prevent corrosion of the disc 10, it may be made froma wide variety of materials. The selection of a material as a sealingmember should be made individually for each installation with cautiontaken to assure the protection of disc 10 from corrosion.

The vacuum support 4 shown with its component members in spacedrelationship in Fig. 4 together with the rupture unit 3 is generallyused on any installation where it is possible that a pressuredifferential will be exerted on the convex side of the rupture unit 3.The vacuum support 4 is of a type as shown in the Simpson et al., PatentNo. 2,523,068, issued September 19, 1950. Since this device isadequately described in the aforementioned United States Letters Patentadditional description here `will be omitted except to mention that itis composed of three main elements. These elements as shown in Fig. 3are a slotted dome-shaped member 22 conforming to the shape of the disc10, a concave-convex disc 23 and a plurality of clips 24 which aresecured to the member 22 to retain the disc 23. The member 22 has slots25 through which pressure may be transmitted to the sealing .member 11.When a vacuum support 4 is used with the safety pressure relief device3, it is sometimes helpful to utilize an additional set of protectionelements 26 which protectthe sealing member 11 from cutting on the sharpedges of the slots 25 in the vacuum member 22.

In operation, the individual elements of the safety pressure reliefdevice 3 and the vacuum support 4 are assembled between two flanges aspreviously described. The pressure on the equipment to be protectedoperates on the concave side of the sealing member 11 through the slots25 in the dome-shaped member 22. When properly assembled, the sealingmember 11 nests in the concave side of the slotted dome-shaped rupturedisc 10 so that the pressure transmitted to the sealing member 11 may beexerted by the sealing member 11 against the concave side of thedome-shaped rupture disc 10. The advantage of the present invention isgained by having a weak section, the convex portion of the rupture disc10, which controls the bursting pressure of the unit but keeping theremainder of the rupture member strong so that even at pressuresapproaching the rupture pressure of the unit there will not be anyappreciable increase in crown height. This result is desinable toprevent any movement of the rupture unit away from the vacuum support.The reason for this small increase in crown height may be Iexplained asresulting from a stronger rupture member in which stresses are below theyield strength of the material except at the weakened sections. Thus atpressures which would normally result in stresses above the yieldstrength in an ordinary rupture unit, the same pressures will only causea minute yield in the weakened section. The same reasoning is rponsiblefor the increased life under conditions which would normally cause acreep failure. Only the weakened section would be stressed enough tocreep and such creep would not appreciably increase the crown height.

Care should be taken in the forming of the rupture disc so that the timelag present in previous devices as previously discussed will beminimized. This is accomplished by pre-bulging the rupture disc to acrown height approaching crown height at rupture. The effect of thispre-bulging is to cold work the rupture disc thereby limiting theyielding of the disc When rupture pressures are reached, thussubstantially cutting down on the time lag.

The present invention operates Ywell when subjected to corrosiveconditions since the sealing member 11 may be made of a material whichis impervious to such conditions, thus protecting the slotteddome-shaped member which determines the bursting pressure from anycorrosion.

What I claim and desire to secure by Letters Patent is:

1. A safety pressure device comprising a dome-shaped rupture memberhaving slots radiating outwardly from a solid central portion andterminating in spaced relation to the periphery of said rupture member,a dome-shaped sealing member, and means positioning said members in apressure relieving area whereby the convex side of said sealing memberis Within and supported by the concave side of said rupture member. v

2. Invention according to claim l, including a plurality of protectionelements said elements being positioned between said rupture member andsaid sealing member in covering relationship to said slots in saidrupture member to protect said sealing member from premature failure dueto abrasion and cutting of said sealing member on the edges of saidslots of said rupture member.

3. Invention according to claim 1, wherein said domeshaped rupturemember is pre-bulged to have a known height less than its. normalunslotted crown height at rupture to provide a substantially lowerrupture pressure than that which would be obtained with normal crownheight.

4. A safety pressure device comprising a dome-shaped rupture memberhaving a plurality of apertures located in spaced relationship aroundthe central portion of said member and a slot radiating from eachaperture, said slots terminating at a position spaced from the peripheryof said rupture member, a dome-shaped sealing member, and meanspositioning said members in a pressure relieving areawhereby the convexside of said sealing member is within and supported by the concave sideof, said rupture member.

5. A safety pressure device comprising `a rupture member having aplurality of slots radiating outwardly from a solid central portion andterminating in spaced relation to the periphery of said rupture member,a rupturable, corrosion-resistant sealing member, said members beingpositioned with respect to each other so that said rupture memberprotects said sealing member from premature rupture and said sealingmember provides a seal for the device and also protects the pressureside of said rupture member from cornosion and, a protection memberpositioned between said rupture member and said sealing member incovering relationship to said slots to protect said sealing member frompremature failure due to abrasion and cutting on the edges of said slotsof said rupture member.

6. A safety pressure relief device comprising a rupture member having apredetermined structural weakness adapted to rupture at a predeterminedpressure, a cornosion resistant seal, said seal having an upper and alower surface, said upper surface of said seal contacting the undersurface of said rupture member, a first protection member positionedbetween said rupture member and said corrosion resistant seal, a slottedsupport having its upper surface in contact with the under surface ofsaid seal, whereby said seal is held against substantial movement at allpressures less than said predetermined pressure, said seal and saidsupport being rupturable at pressures not greater than saidpredetermined pressure, and a second protection member positionedbetween said seal and said support in covering relation to the slots insaid support, said protection members protecting said seal frompremature failure due to abrasion and cutting on said rupture member andsaid slotted support.

7. A safety pressure relief device comprising a rupture member having aplurality of slots radiating outwardly from a solid central portion andterminating in spaced relation to the periphery of said rupture member,a rup turable sealing member, said members being positioned with respectto each other so that said rupture member protects said sealing memberfrom premature rupture and said sealing member provides a seal -for thedevice and a plurality of protection members positioned between saidrupture member Aand said sealing member in covering relationship to saidslots to protect said sealing member from premature failure due toabrasion and cutting on the edges of said slots of said rupture member,each of said protection members Ibeing secured to said rupture memberalong one edge of the slot which said member covers.

8. A safety pressure device comprising a dome-shaped rupture memberhaving openings dening lines ofpredetermined structural weaknessradiating outwardly from a solid central portion and terminating inspaced relation to the periphery of said rupture member, a dome-shapedsealing member, and means positioning said members in a pressurerelieving larea whereby the convex side of said sealing member is withinand supported by the concave side of said rupture member.

9. A safety pressure device comprising a dome-shaped rupture memberhaving slots extending generally outward from a solid central portionand terminating in spaced relation to the periphery of said rupturemember, a dome-shaped sealing member, and means positioning said membersin a pressure relieving area whereby the convex side of said sealingmember is within and supported by the concave side of said rupturemember.

References Cited in the le of this patent UNITED STATES PATENTS 138,171Matthews Apr. 22, 1873 328,008 Conner et al. Oct. 13, 1885 2,123,662Raymond July 12, 1938 2,523,068 Simpson et al. Sept. 19, 1950 2,548,744Simms Apr. 10, 1951 2,656,950 Coffman Oct. 27, 1953 2,758,749 Jones Aug.14, 1956 UNITED STATES PATENT OFFICE CERTIFICATION OE CORRECTION PatentNo. 2,953,279 September 20, 1%0

Robert S. Coffman It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 4, line 63, for "known" read crown Signed and sealed this 25thday of April 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner Of Patents

